In MW 1.23wmf17, when requesting the paraminfo for the revisiondelete module, the errors list appears malformed. In addition to the typical array ( 'code' => ..., 'desc' => ... ) error structures, it contains also two strings:
A target title is required for this RevDel type
Bad value for some parameter
I guess that for these only the 'desc' part gets inserted instead of the entire error structure.